Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
In some LEDs the growth substrate remains part of the final device structure, for example to provide mechanical stability to the semiconductor structure. A significant amount of light may be emitted through the sides of the growth substrate. Side light emission from the substrate is undesirable in applications that require or prefer that most or all of the light be emitted from the top of the device.
US 2010/0267219 describes a method of thinning the growth substrate. According to the abstract, the method includes “a sapphire substrate grinding step of grinding the back side of the sapphire substrate; a modified layer forming step of applying a laser beam to the sapphire substrate from the back side thereof to thereby form a modified layer in the sapphire substrate along each street, . . . and a wafer dividing step of breaking the sapphire substrate along each street where the modified layer is formed”.